Electronic devices use power to operate. A switched mode power converter is commonly used to power such electronic devices due to its high efficiency, small size, and low weight. Conventional wall sockets provide a high voltage alternating current. A switching power converter converts a high voltage alternating current (ac) input to provide a regulated direct current (dc) output using an energy transfer element. Switching power converters typically include a power converter controller. The power converter controller provides output regulation by sensing the output and controlling the regulated dc output using a closed loop. During operation, a switch is utilized to provide the desired output by varying the duty cycle (typically the ratio of the on time of the switch to the total switching period) of the switch in a switched mode power converter (also referred as a switching power supply or a switched mode power supply).
In lighting applications, LED lamps are quickly replacing traditional incandescent lamps due in part to the lower power consumption and longer lifetime of LED lamps. In general, LED lamps require a regulated power converter to provide a regulated current and voltage from the ac power line. LEDs are generally current driven devices and the brightness of an LED lamp is proportional to the amount of current provided to the LED lamp. In general, the more current flowing through the LED lamp corresponds to a brighter LED lamp. As such, dimming may be accomplished by varying the amount of current provided the LED lamp.
As noted above, power converters may use a controller to provide output regulation to an electrical device (such as an LED lamp) by sensing and controlling the output of the power converter in a closed loop. More specifically, the controller is coupled to a sensor that provides feedback information about the output of the power converter in order to regulate the output quantity delivered to the LED lamp (also referred to as a load). The controller regulates the output quantity delivered to the load by controlling a switch to turn on and off in response to the feedback information from the sensor to transfer energy pulses to the power converter output from a source of input power such as a power line. For LED lamps, the power converter regulates the output current to the LED lamp. For dimming applications, a dimming control signal representative of how much the power converter should dim the LED lamp is provided to the power converter. As mentioned above, dimming may be accomplished by varying the amount of current provided the LED lamp. As such, the dimming control signal can modify the feedback information to subsequently lower the output current delivered to an LED lamp and thus dim the LED lamp.